Aniline is a commodity in the chemical industry, widely used in the preparation of dyes, pigments and chemical intermediates. A large proportion of the aniline consumed is produced by hdrogenation of nitrobenzene (NB), which normally contains polynitrophenol (PNP) impurities, chiefly 2,4-dinitrophenol and picric acid. It was heretofore thought desirable that these PNP impurities be removed from the NB before hydrogenation, and this was normally done by extracting them with alkaline water. Although this is a satisfactory method, the PNP impurities are extremely toxic and disposing of them is difficult and expensive.
It has now been found that this extraction of PNP impurities can be dispensed with entirely and that aniline can be prepared by catalytic hydrogenation directly from NB containing these PNP impurities. This converts the PNP impurities to polymeric tars which can be easily separated from the aniline product and disposed of, most preferably by incineration. This is especially advantageous because the NB/aniline reaction itself produces tars, which must be separated from the aniline and disposed of. Thus, when the process of the invention is used, the two types of tar can be separated from the NB product and disposed of together. The costly and time-consuming PNP separation step is thereby eliminated.